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Weed of the Month: Field Horsetail (Equisetum arvense)

Posted: May 7, 2012

Field horsetail is part of the ancient genus Equisetum, which was the dominant plant group during the Carboniferous age more than 230 million years ago. It looks like the prehistoric survivor that it is, and can be one of the toughest weeds to manage.

Field Horsetail

Field horsetail is found growing in landscape beds, fields, wooded areas and along roadsides. It is often found in moist soils, but can grow well in drier places once established, and is a common problem in gravelly soils along roadsides and railroad tracks. Field horsetail contains high levels of silica, giving rise to another common name: scouring rush; it also makes it toxic to livestock.

What is Field Horsetail?

Field horsetail is a perennial that grows from a tuber-bearing rhizome. Two types of stems grow from the rhizome annually. Tan-to-white fertile stems grow in early spring, resembling short asparagus sprouts, up to a foot tall. They are unbranched and leafless, topped by a spore-bearing cone that can be up to four inches long. Since they lack chlorophyll, they die shortly after releasing their spores. Sterile stems arise after the fertile stems die back, growing about two feet tall. These stems are grooved and hollow, covered with whirls of feathery leaves that make it look like a green bottlebrush or a miniature conifer.

Fleshy tubers grow along the underground rhizomes singly or in pairs, and are positioned from a few inches to six feet deep in the soil. They store carbohydrates produced by photosynthesis, allowing field horsetail to have amazing regenerative capability and making it difficult to control.

Controlling Field Horsetail

Control options include repeated mowing or mechanical removal. Although it can take years, dedicated removal of sterile stems depletes the carbohydrate reserves and will eventually exhaust the rhizome. Field horsetail grows best in full sun, and can also be controlled by shading. Mechanical removal of the stems followed by mulching with black plastic can also be effective. Tillage can make the problem worse by spreading the rhizomes and/or tubers.

As for herbicides, the active ingredient halosulfuron-methyl (Sedgehammer) can be effective, and Sedgehammer is labeled to control field horsetail in landscape areas. It should be applied before the sterile stems are six inches tall for maximum control. In right-of-way situations, diclobenil (Casaron), clorsulfuron (Telar), and sulfometuron (Oust) are labeled for control. Be sure to read and follow the label prior to using any of these herbicides.